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man pages->IRIX man pages -> complib/ssptri (3)
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### Contents

```
SSPTRI(3F)							    SSPTRI(3F)

```

### NAME[Toc][Back]

```     SSPTRI - compute the inverse of a real symmetric indefinite matrix	A in
packed storage using the factorization A =	U*D*U**T or A =	L*D*L**T
computed by SSPTRF
```

### SYNOPSIS[Toc][Back]

```     SUBROUTINE	SSPTRI(	UPLO, N, AP, IPIV, WORK, INFO )

CHARACTER	UPLO

INTEGER	INFO, N

INTEGER	IPIV( *	)

REAL		AP( * ), WORK( * )
```

### PURPOSE[Toc][Back]

```     SSPTRI computes the inverse of a real symmetric indefinite	matrix A in
packed storage using the factorization A =	U*D*U**T or A =	L*D*L**T
computed by SSPTRF.

```

### ARGUMENTS[Toc][Back]

```     UPLO    (input) CHARACTER*1
Specifies whether the details of the factorization	are stored as
an	upper or lower triangular matrix.  = 'U':  Upper triangular,
form is A = U*D*U**T;
= 'L':  Lower triangular, form is A = L*D*L**T.

N	     (input) INTEGER
The order of the matrix A.	 N >= 0.

AP	     (input/output) REAL array,	dimension (N*(N+1)/2)
On	entry, the block diagonal matrix D and the multipliers used to
obtain the	factor U or L as computed by SSPTRF, stored as a
packed triangular matrix.

On	exit, if INFO =	0, the (symmetric) inverse of the original
matrix, stored as a packed	triangular matrix. The j-th column of
inv(A) is stored in the array AP as follows:  if UPLO = 'U', AP(i
+ (j-1)*j/2) = inv(A)(i,j)	for 1<=i<=j; if	UPLO = 'L', AP(i +
(j-1)*(2n-j)/2) = inv(A)(i,j) for j<=i<=n.

IPIV    (input) INTEGER array, dimension (N)
Details of	the interchanges and the block structure of D as
determined	by SSPTRF.

WORK    (workspace) REAL array, dimension (N)

INFO    (output) INTEGER
= 0: successful exit
< 0: if INFO = -i,	the i-th argument had an illegal value

Page 1

SSPTRI(3F)							    SSPTRI(3F)

> 0: if INFO = i, D(i,i) =	0; the matrix is singular and its
inverse could not be computed.
SSPTRI(3F)							    SSPTRI(3F)

```

### NAME[Toc][Back]

```     SSPTRI - compute the inverse of a real symmetric indefinite matrix	A in
packed storage using the factorization A =	U*D*U**T or A =	L*D*L**T
computed by SSPTRF
```

### SYNOPSIS[Toc][Back]

```     SUBROUTINE	SSPTRI(	UPLO, N, AP, IPIV, WORK, INFO )

CHARACTER	UPLO

INTEGER	INFO, N

INTEGER	IPIV( *	)

REAL		AP( * ), WORK( * )
```

### PURPOSE[Toc][Back]

```     SSPTRI computes the inverse of a real symmetric indefinite	matrix A in
packed storage using the factorization A =	U*D*U**T or A =	L*D*L**T
computed by SSPTRF.

```

### ARGUMENTS[Toc][Back]

```     UPLO    (input) CHARACTER*1
Specifies whether the details of the factorization	are stored as
an	upper or lower triangular matrix.  = 'U':  Upper triangular,
form is A = U*D*U**T;
= 'L':  Lower triangular, form is A = L*D*L**T.

N	     (input) INTEGER
The order of the matrix A.	 N >= 0.

AP	     (input/output) REAL array,	dimension (N*(N+1)/2)
On	entry, the block diagonal matrix D and the multipliers used to
obtain the	factor U or L as computed by SSPTRF, stored as a
packed triangular matrix.

On	exit, if INFO =	0, the (symmetric) inverse of the original
matrix, stored as a packed	triangular matrix. The j-th column of
inv(A) is stored in the array AP as follows:  if UPLO = 'U', AP(i
+ (j-1)*j/2) = inv(A)(i,j)	for 1<=i<=j; if	UPLO = 'L', AP(i +
(j-1)*(2n-j)/2) = inv(A)(i,j) for j<=i<=n.

IPIV    (input) INTEGER array, dimension (N)
Details of	the interchanges and the block structure of D as
determined	by SSPTRF.

WORK    (workspace) REAL array, dimension (N)

INFO    (output) INTEGER
= 0: successful exit
< 0: if INFO = -i,	the i-th argument had an illegal value

Page 1

SSPTRI(3F)							    SSPTRI(3F)

> 0: if INFO = i, D(i,i) =	0; the matrix is singular and its
inverse could not be computed.

PPPPaaaaggggeeee 2222```
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